MEI S1; anyone else find . . . Watch

~Bex~
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#21
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#21
(Original post by mrsmiley)
Did anybody get the probabilty of the paintings all being done wrongly, and then correctly as 5.?*10^-5. I almost ran out of time.
Yeh, I got that. I thought it was wrong at the time because it seemed ridiculously small, but I've seen a few posts from people saying they got that, so I feel happier. When I first looked at that question I got so confused lol, but it wasn't really that bad once you knew what it was asking.
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Nitrox
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#22
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#22
do you think they will lower the grade boundaries
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~Bex~
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#23
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#23
(Original post by ammar89)
that cant be right because 0.8 has to be in the equation
1-0.8=0.2
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Gaz Coombes
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#24
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#24
Ah crap seems ive got a lot wrong. Hope the grade boundaries aren't high.
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Gaz Coombes
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#25
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#25
Ah crap seems ive got a lot wrong. Hope the grade boundaries aren't high. Did everyone get variance as 1.08?
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~Bex~
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#26
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#26
(Original post by Gaz Coombes)
Ah crap seems ive got a lot wrong. Hope the grade boundaries aren't high. Did everyone get variance as 1.08?
I think that's what I got, can't remember for certain though.
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Gaz Coombes
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#27
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#27
What do people think the grade boundaries will be?
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Nitrox
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#28
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#28
here is a very similar question to the one in the exam

how large a sample would be needed for the probability of it containing at least one allergic person to be greater than 99.9%

answer

1 - (0.75)n is greater than (cant find inequal signs) 0.999
(0.75)n is less than 0.001
(0.75)n = 0.001
n log 0.75 = log 0.001
n = log 0.001/log0.75
=24.01
so 25 people

did you use the same method
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Aired
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#29
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#29
I think the grade boundaries will be relatively normal. There were some difficult questions, but the rest of them weren't too bad (i.e. the expectance & variance question was just free marks if you knew the formulae...).

For the rock one I think you had something like probability of finding a fossil is 0.1 and they wanted at least 80% chance of finding at least one

P(Finding at least one) = 1 - P(Finding none)
= 1 - (0.9)^n (With n being the number of rocks)

Want at least an 80% chance

.`. 1 - (0.9)^n > 0.8
(0.9)^n < 0.2
nlog0.9 < log0.2
n > (log0.2)/(log0.9)
n > 15.28

Therefore he needs to check 16 rocks minimum.

You can check this by putting it back into the original equation

P(Finding at least 1) = 1 - (0.9)^16
= 1 - 0.185
= 0.815
= 81.5%
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Nitrox
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#30
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#30
im gutted now
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Aired
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#31
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#31
Wasn't it only 2 or 3 marks? Don't worry about it
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Gaz Coombes
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#32
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#32
3 marks. Teachers are saying it was hard so I predict low boundaries!
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Nitrox
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#33
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#33
the thing is i got 16 but then i changed it!
and i did the same for the portrait question - 7 marks lost easilly
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Gaz Coombes
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#34
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#34
Don't need 100% for a good grade.
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Nitrox
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#35
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#35
i want and need an A
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#36
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#36
You can lose like 18 marks and still get an A
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Nitrox
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#37
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#37
how did you work out the hypotheses question with n =30
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Gaz Coombes
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#38
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#38
Was n 30. I thought it was 20!
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~Bex~
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#39
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#39
well it was for less than or equal to two, and you'd already worked it out for 0 and 1 in the previous question, so you just work it out for two and add them all up
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Aired
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#40
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#40
You just did P(0) + P(1) + P(2) (using the binomial distribution)
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